The project goal is to characterize the pathways leading to formation of surface membrane-bound IgG or to secretion of IgG in a cloned, murine myeloma cell line. The surface Ig ("Ig-mem") and secreted Ig are separate end-products derived from a common intracellular precursor. Techniques developed for identifying intermediates and end-products of each pathway will be applied to analysis of B-lymphocyte differentiation during normal humoral immune responses. It will be determined whether normal cells exist which integrate IgG into surface membrane by a pathway analogous to Ig-mem formation in myeloma cells. The functioning of surface IgG on normal cells as specific antigen-sensitive receptor will be examined. These studies would provide evidence for existence of intermediate cellular stages of B-lymphocyte differentiation expressing Ig-mem. The effects of specific elimination of such cells can be assessed in terms of its usefulness as a strategy for regulation of the humoral immune response.